Active Intermediates in Ethylene Polymerization over Titanium Bis(phenoxyimine) Catalysts

Abstract

Reactive intermediates in living olefin polymerization over homogeneous catalysts based on bis[N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato]titanium(IV) dichloride (L2TiCl2) have been studied. Outer sphere ion pairs [L2TiMe(S)]+[Me-MAO]- and [L2TiMe(S)]+[B(C6F5)4]- (S = solvent molecule), formed by activation of L2TiCl2 with MAO or with AlMe3/[CPh3]+[B(C6F5)4]-, and reactions of these ion pairs with ethene to afford chain-propagating species [L2TiP]+[Me-MAO]- and [L2TiP]+[B(C6F5)4]- (P = growing polymeryl chain) have been characterized by 1H, 13C, and 19F NMR spectroscopy

UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

“…Although, data on the effect of Al/Ti over polymerization is scarce for this type of catalyst, a similar dependence has been described by other authors [41,42]. On the other hand, a stronger decay of the instantaneous activity seems to occur at the highest Al/Ti ratios ( Figure S4, right plot, in Supporting Information) therefore, the role that may play the increasing concentration of trimethylaluminum, invariably present in MAO, in deactivation of FI catalyst should not be neglected [43,44].…”

“…It is well known from literature that titanium FI-catalysts are very sensitive toward trimethylaluminum (TMA), which is always present in the co-catalyst MAO [43,44]. The proposed deactivation pathway is depicted in Scheme 4 [35].…”

An EPR Study of the V(IV) Species Formed Upon Activation of a Vanadyl Phenoxyimine Polymerization Catalyst with AlR3 and AlR2Cl (R = Me, Et)

“…For related complexes of zirconium and titanium, such phenoxyimine ligand scrambling starts at temperatures higher than À30 8C. [22][23][24] Therefore, 1-AlEt 3 is the adduct of AlEt 3 with 1, which can be presented as (L 0 ) 2 V IV (O)(AlEt 3 ). We have used the notation L 0 for the phenoxyimine ligand to show that the initial ligand L can be modified via interaction of AlEt 3 with the four OH groups of L. This transformation occurs far from the metal center and barely affects the reactivity of the vanadium catalyst or its EPR spectrum.…”

“…The reaction of phenoxyimine complexes of zirconium and titanium with the excess of AlMe 3 results in the rapid transfer of the phenoxyimine ligand to aluminum at 20 8C. [22][23][24] By analogy, one can suggest that in complexes 2 and 3 one of the phenoxyimine ligands is replaced by Et-anion and they can be schematically presented as L 0 V IV (O)(Et)(AlEt 3 ) (Scheme 2). We have tried to prove the incorporation of the V --O moiety into composition of complexes 2 and 3 by IR spectroscopy.…”

Scalar Coupling Across [CH⋅⋅⋅FC] Interactions in (σ‐Aryl)‐Chelating Post‐Metallocenes

“…[11] Furthermore, although experimental findings indicate that the influence of the ortho-fluorine groups is not steric in nature, [3,8] computational studies suggest that repulsive o-F À polymer contacts dominate and any C À H···F À C interactions are minimal. [12] Hence, although the living propagating species has been observed in solution by NMR spectroscopy, [13,14] verification of the proposed CÀ H···FÀC interactions remains elusive. More generally, notwithstanding the ongoing debate regarding the nature and significance of dispersion-dominated C À H···F À C hydrogen bonds, [15,16] interest in these interactions have proliferated in recent years and they are habitually invoked in such diverse fields as crystal engineering, [17] materials science, [18] rotational [19] and vibrational [20] spectroscopy, theoretical studies (including calculation and estimation of bond energies), [21] and biomolecular design and recognition.…”